1. Field of the Invention
An embodiment of the present invention relates to a moving-object tracking control apparatus for controlling tracking of a moving object moving on a screen. Another embodiment of the present invention relates to a system including the moving-object tracking control apparatus.
A further embodiment of the present invention relates to a method and program for implementing the moving-object tracking control function.
2. Description of the Related Art
In monitoring systems, the capability (tracking capability) of tracking a moving target (e.g., a person, a vehicle, or other objects) through images on the screen captured by an imaging apparatus, such as a monitoring camera, is important. For example, when a monitoring camera is used to monitor a “keep out” zone, it is important to track and record the behavior of an intruder in the zone.
A monitoring camera whose imaging direction is fixed can detect and track an intruder by using a moving-object detection technique (e.g., C. Stuffer, W. E. L. Grimson, “Adaptive background mixture models for real-time tracking”).
However, the fixed monitoring camera can only track an intruder within its imaging coverage. If the intruder moves outside the imaging coverage of the camera, the camera can no longer track the intruder.
Therefore, movable monitoring systems of the type in which the imaging direction of monitoring cameras is variable have been used. In a movable monitoring system, a monitoring camera is mounted on a rotating turntable to expand the tracking area beyond the imaging coverage of the camera. The monitoring camera is rotated in accordance with the movement of an intruder so that the intruder can be constantly shot within the imaging coverage of the camera.
In the movable monitoring systems, however, it is difficult to detect an intruder using the above-described moving-object detection processing during the rotation of the camera. In the moving-object detection processing, moving objects, such as an intruder, are defined as the foreground objects while other objects are defined as the background objects, and a moving target is detected on the assumption of the stationary background and the moving foreground. In the movable monitoring systems, however, both foreground objects and background objects move in accordance with the rotation of the imaging camera, and thus the assumption of the moving-object detection processing is not satisfied.
The tracking operation with a monitoring camera rotated may be divided into two phases, that is, a moving-object detecting phase and a moving-object tracking phase.
The moving-object detecting phase is a processing phase for performing the above-described moving-object detection processing in a state where the monitoring camera is held stationary to detect a moving object or target to be tracked. When the moving target is detected, a transition to the moving-object tracking phase occurs, and the moving target is tracked with the imaging camera rotated. In the moving-object tracking phase, a method capable of detecting the moving target even during the rotation of the monitoring camera is employed. At the end of the moving-object tracking procedure, the imaging camera is stopped, and a transition back to the moving-object detecting phase occurs.
A moving-object detection method of the related art employed in the moving-object detecting phase is disclosed in Japanese Unexamined Patent Application Publication No. 2003-39387. In this method, motion vectors are calculated for a target to be tracked and its surrounding area, and a motion vector to be tracked is determined. FIG. 1 shows an example of the motion vectors determined by this detection method. As shown in FIG. 1, in this moving-object detection method, since the motion vectors determined for a target to be tracked (in this example, a person) differ from those for the background objects behind the target, the difference therebetween is utilized to select only the motion vectors for the target. This detection method enables the determination of the position of the target to be tracked even during the rotation of the imaging camera.